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Discussion Starter · #1 ·
Well, the bike has been running great all season when all of a sudden on a ride last week, the bike started backfiring through the throttle bodies at about 2500-3500RPM making the bike buck and stumble. It had never done that before. I did get the occasional hiccup once in a while but at random rpms and very infrequently. These backfires through the throttle bodies are pretty violent and can be felt though the throttle cable and handle. I took the fairings off and took a look for any kinked lines or obstructions, took the air filter off and ran the bike, when it was run in the 2500-3500 rpm range, you can see the fireworks shoot up the air hose back into the air box.

please help!

Most threads talk about backfiring due to a lean condition but through the exhaust. This is starting to get scary

6000 mi service done 1500 mi ago
Mods are as follows
Open airbox lid
k&n air filter
Termignoni High mount Slip ons
header wrap.
 

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Discussion Starter · #2 ·
took off timing belt covers today to see if it may be a timing problem. Well one of the bolts holding down the belt tensioner on the horizontal cylinder worked its way out. rollers were on the proper timing marks still. Readjusted tension (allen key method) and secured the tensioner bolts. started the bike but still get violent backfiring up the throttle bodies at about 2500rpm. Check for any leaks around intake and throttle bodies with carb cleaner to see if there was any racing. Does not appear to be any leaks.

HELP!!
 

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i think i have your same problem! i've never seen flames but from 2 to 4k rpm, sometimes the engine gives a blow (its very noisy) and i feel like if the throttle bodies were opened because the gas wire tension seems to get lower for a sec.
i have 13k km and in the last check they've registered valves, and my belts aren't loosen!
i'm looking for the solution of this problem, but i really can't understand what it is...

ps. it doesn't do it every time, only sometimes when i open the gas from idle or like that
 

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Check your plugs. Plugs may have carbon buildup that can retain heat and cause pre-ignition, or may be in the wrong heat range / damaged.
 

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Have you done a compression/leakdown test? When that belt tension slackened your valves may have met the pistons and caused a leak at the valve seat.

Other than that you may have an issue that you need the Mathesis to diagnose. When I had a similar problem (without the added variable of the loose belt) the air pressure sensor in the ECU went. No way for me to diagnose without the Mathesis to tell me the sensor was gone.
 
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